Signal transduction pathways of angiotensin II--induced c-fos gene expression in cardiac myocytes in vitro. Roles of phospholipid-derived second messengers

Mechanisms underlying divergent relationships between Ca2+ and YAP/TAZ signalling

Yes-associated protein (YAP) and its homologue TAZ are transducers of several biochemical and biomechanical signals, integrating multiplexed inputs from the microenvironment into higher level cellular functions such as proliferation, differentiation and migration. Emerging evidence suggests that Ca2+ is a key second messenger that connects microenvironmental input signals and YAP/TAZ regulation. However, studies that directly modulate Ca2+ have reported contradictory YAP/TAZ responses: in some studies, a reduction in Ca2+ influx increases the activity of YAP/TAZ, while in others, an increase in Ca2+ influx activates YAP/TAZ. Importantly, Ca2+ and YAP/TAZ exhibit distinct spatiotemporal dynamics, making it difficult to unravel their connections from a purely experimental approach. In this study, we developed a network model of Ca2+ -mediated YAP/TAZ signalling to investigate how temporal dynamics and crosstalk of signalling pathways interacting with Ca2+ can alter the YAP/TAZ response, as observed in experiments. By including six signalling modules (e.g. GPCR, IP3-Ca2+ , kinases, RhoA, F-actin and Hippo-YAP/TAZ) that interact with Ca2+ , we investigated both transient and steady-state cell response to angiotensin II and thapsigargin stimuli. The model predicts that stimuli, Ca2+ transients and frequency-dependent relationships between Ca2+ and YAP/TAZ are primarily mediated by cPKC, DAG, CaMKII and F-actin. Simulation results illustrate the role of Ca2+ dynamics and CaMKII bistable response in switching the direction of changes in Ca2+ -induced YAP/TAZ activity. A frequency-dependent YAP/TAZ response revealed the competition between upstream regulators of LATS1/2, leading to the YAP/TAZ non-monotonic response to periodic GPCR stimulation. This study provides new insights into underlying mechanisms responsible for the controversial Ca2+ -YAP/TAZ relationship observed in experiments. KEY POINTS: YAP/TAZ integrates biochemical and biomechanical inputs to regulate cellular functions, and Ca2+ acts as a key second messenger linking cellular inputs to YAP/TAZ. Studies have reported contradictory Ca2+ -YAP/TAZ relationships for different cell types and stimuli. A network model of Ca2+ -mediated YAP/TAZ signalling was developed to investigate the underlying mechanisms of divergent Ca2+ -YAP/TAZ relationships. The model predicts context-dependent Ca2+ transient, CaMKII bistable response and frequency-dependent activation of LATS1/2 upstream regulators as mechanisms governing the Ca2+ -YAP/TAZ relationship. This study provides new insights into the underlying mechanisms of the controversial Ca2+ -YAP/TAZ relationship to better understand the dynamics of cellular functions controlled by YAP/TAZ activity.

Synergistic action of organophosphates and COVID-19 on inflammation, oxidative stress, and renin-angiotensin system can amplify the risk of cardiovascular maladies

Organophosphates (OPs) are ubiquitous environmental contaminants, widely used as pesticides in agricultural fields. In addition, they serve as flame-retardants, plasticizers, antifoaming or antiwear agents in lacquers, hydraulic fluids, and floor polishing agents. Therefore, world-wide and massive application of these compounds have increased the risk of unintentional exposure to non-targets including the human beings. OPs are neurotoxic agents as they inhibit the activity of acetylcholinesterase at synaptic cleft. Moreover, they can fuel cardiovascular issues in the form of myocardities, cardiac oedema, arrhythmia, systolic malfunction, infarction, and altered electrophysiology. Such pathological outcomes might increase the severity of cardiovascular diseases which are the leading cause of mortality in the developing world. Coronavirus disease-19 (COVID-19) is the ongoing global health emergency caused by SARS-CoV-2 infection. Similar to OPs, SARS-CoV-2 disrupts cytokine homeostasis, redox-balance, and angiotensin-II/AT₁R axis to promote cardiovascular injuries. Therefore, during the current pandemic milieu, unintentional exposure to OPs through several environmental sources could escalate cardiac maladies in patients with COVID-19.

Angiotensin II-Induced Signal Transduction Mechanisms for Cardiac Hypertrophy

Although acute exposure of the heart to angiotensin (Ang II) produces physiological cardiac hypertrophy and chronic exposure results in pathological hypertrophy, the signal transduction mechanisms for these effects are of complex nature. It is now evident that the hypertrophic response is mediated by the activation of Ang type 1 receptors (AT₁R), whereas the activation of Ang type 2 receptors (AT₂R) by Ang II and Mas receptors by Ang-(1-7) exerts antihypertrophic effects. Furthermore, AT₁R-induced activation of phospholipase C for stimulating protein kinase C, influx of Ca²⁺ through sarcolemmal Ca²⁺- channels, release of Ca²⁺ from the sarcoplasmic reticulum, and activation of sarcolemmal NADPH oxidase 2 for altering cardiomyocytes redox status may be involved in physiological hypertrophy. On the other hand, reduction in the expression of AT₂R and Mas receptors, the release of growth factors from fibroblasts for the occurrence of fibrosis, and the development of oxidative stress due to activation of mitochondria NADPH oxidase 4 as well as the depression of nuclear factor erythroid-2 activity for the occurrence of Ca²⁺-overload and activation of calcineurin may be involved in inducing pathological cardiac hypertrophy. These observations support the view that inhibition of AT₁R or activation of AT₂R and Mas receptors as well as depression of oxidative stress may prevent or reverse the Ang II-induced cardiac hypertrophy.

The role of angiotensin II and relaxin in vascular adaptation to pregnancy

In brief

There is a pregnancy-induced vasodilation of blood vessels, which is known to have a protective effect on cardiovascular function and can be maintained postpartum. This review outlines the cardiovascular changes that occur in a healthy human and rodent pregnancy, as well as different pathways that are activated by angiotensin II and relaxin that result in blood vessel dilation.

Abstract

During pregnancy, systemic and uteroplacental blood flow increase to ensure an adequate blood supply that carries oxygen and nutrients from the mother to the fetus. This results in changes to the function of the maternal cardiovascular system. There is also a pregnancy-induced vasodilation of blood vessels, which is known to have a protective effect on cardiovascular health/function. Additionally, there is evidence that the effects of maternal vascular vasodilation are maintained post-partum, which may reduce the risk of developing high blood pressure in the next pregnancy and reduce cardiovascular risk later in life. At both non-pregnant and pregnant stages, vascular endothelial cells produce a number of vasodilators and vasoconstrictors, which transduce signals to the contractile vascular smooth muscle cells to control the dilation and constriction of blood vessels. These vascular cells are also targets of other vasoactive factors, including angiotensin II (Ang II) and relaxin. The binding of Ang II to its receptors activates different pathways to regulate the blood vessel vasoconstriction/vasodilation, and relaxin can interact with some of these pathways to induce vasodilation. Based on the available literature, this review outlines the cardiovascular changes that occur in a healthy human pregnancy, supplemented by studies in rodents. A specific focus is placed on vasodilation of blood vessels during pregnancy; the role of endothelial cells and endothelium-derived vasodilators will also be discussed. Additionally, different pathways that are activated by Ang II and relaxin that result in blood vessel dilation will also be reviewed.

Gut microbiota production of trimethyl-5-aminovaleric acid reduces fatty acid oxidation and accelerates cardiac hypertrophy

Numerous studies found intestinal microbiota alterations which are thought to affect the development of various diseases through the production of gut-derived metabolites. However, the specific metabolites and their pathophysiological contribution to cardiac hypertrophy or heart failure progression still remain unclear. N,N,N-trimethyl-5-aminovaleric acid (TMAVA), derived from trimethyllysine through the gut microbiota, was elevated with gradually increased risk of cardiac mortality and transplantation in a prospective heart failure cohort (n = 1647). TMAVA treatment aggravated cardiac hypertrophy and dysfunction in high-fat diet-fed mice. Decreased fatty acid oxidation (FAO) is a hallmark of metabolic reprogramming in the diseased heart and contributes to impaired myocardial energetics and contractile dysfunction. Proteomics uncovered that TMAVA disturbed cardiac energy metabolism, leading to inhibition of FAO and myocardial lipid accumulation. TMAVA treatment altered mitochondrial ultrastructure, respiration and FAO and inhibited carnitine metabolism. Mice with γ-butyrobetaine hydroxylase (BBOX) deficiency displayed a similar cardiac hypertrophy phenotype, indicating that TMAVA functions through BBOX. Finally, exogenous carnitine supplementation reversed TMAVA induced cardiac hypertrophy. These data suggest that the gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent FAO.

Intestinal microbiota alterations may affect heart function through the production of gut-derived metabolites. Here the authors found that gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent fatty acid oxidation.

Between Inflammation and Autophagy: The Role of Leptin-Adiponectin Axis in Cardiac Remodeling

Cardiac remodeling is the process by which the heart adapts to stressful stimuli, such as hypertension and ischemia/reperfusion; it ultimately leads to heart failure upon long-term exposure. Autophagy, a cellular catabolic process that was originally considered as a mechanism of cell death in response to detrimental stimuli, is thought to be one of the main mechanisms that controls cardiac remodeling and induces heart failure. Dysregulation of the adipokines leptin and adiponectin, which plays essential roles in lipid and glucose metabolism, and in the pathophysiology of the neuroendocrine and cardiovascular systems, has been shown to affect the autophagic response in the heart and to contribute to accelerate cardiac remodeling. The obesity-associated protein leptin is a pro-inflammatory, tumor-promoting adipocytokine whose elevated levels in obesity are associated with acute cardiovascular events, and obesity-related hypertension. Adiponectin exerts anti-inflammatory and anti-tumor effects, and its reduced levels in obesity correlate with the pathogenesis of obesity-associated cardiovascular diseases. Leptin- and adiponectin-induced changes in autophagic flux have been linked to cardiac remodeling and heart failure. In this review, we describe the different molecular mechanisms of hyperleptinemia- and hypoadiponectinemia-mediated pathogenesis of cardiac remodeling and the involvement of autophagy in this process. A better understanding of the roles of leptin, adiponectin, and autophagy in cardiac functions and remodeling, and the exact signal transduction pathways by which they contribute to cardiac diseases may well lead to discovery of new therapeutic agents for the treatment of cardiovascular remodeling.

Upregulation of Rubicon promotes autosis during myocardial ischemia/reperfusion injury

Although autophagy is generally protective, uncontrolled or excessive activation of autophagy can be detrimental. However, it is often difficult to distinguish death by autophagy from death with autophagy, and whether autophagy contributes to death in cardiomyocytes (CMs) is still controversial. Excessive activation of autophagy induces a morphologically and biochemically defined form of cell death termed autosis. Whether autosis is involved in tissue injury induced under pathologically relevant conditions is poorly understood. In the present study, myocardial ischemia/reperfusion (I/R) induced autosis in CMs, as evidenced by cell death with numerous vacuoles and perinuclear spaces, and depleted intracellular membranes. Autosis was observed frequently after 6 hours of reperfusion, accompanied by upregulation of Rubicon, attenuation of autophagic flux, and marked accumulation of autophagosomes. Genetic downregulation of Rubicon inhibited autosis and reduced I/R injury, whereas stimulation of autosis during the late phase of I/R with Tat-Beclin 1 exacerbated injury. Suppression of autosis by ouabain, a cardiac glycoside, in humanized Na+,K+-ATPase-knockin mice reduced I/R injury. Taken together, these results demonstrate that autosis is significantly involved in I/R injury in the heart and triggered by dysregulated accumulation of autophagosomes due to upregulation of Rubicon.

Increase in PKCα Activity during Heart Failure Despite the Stimulation of PKCα Braking Mechanism

Rationale: Heart failure (HF) is marked by dampened cardiac contractility. A mild therapeutic target that improves contractile function without desensitizing the β-adrenergic system during HF may improve cardiac contractility and potentially survival. Inhibiting protein kinase C α (PKCα) activity may fit the criteria of a therapeutic target with milder systemic effects that still boosts contractility in HF patients. PKCα activity has been observed to increase during HF. This increase in PKCα activity is perplexing because it is also accompanied by up-regulation of a molecular braking mechanism. Objective: I aim to explore how PKCα activity can be increased and maintained during HF despite the presence of a molecular braking mechanism. Methods and Results: Using a computational approach, I show that the local diacylglycerol (DAG) signaling is regulated through a two-compartment signaling system in cardiomyocytes. These results imply that after massive myocardial infarction (MI), local homeostasis of DAG signaling is disrupted. The loss of this balance leads to prolonged activation of PKCα, a key molecular target linked to LV remodeling and dysfunctional filling and ejection in the mammalian heart. This study also proposes an explanation for how DAG homeostasis is regulated during normal systolic and diastolic cardiac function. Conclusions: I developed a novel two-compartment computational model for regulating DAG homeostasis during Ang II-induced heart failure. This model provides a promising tool with which to study mechanisms of DAG signaling regulation during heart failure. The model can also aid in identification of novel therapeutic targets with the aim of improving the quality of life for heart failure patients.

Effect of Docosahexaenoic Acid on Ca2+ Signaling Pathways in Cerulein-Treated Pancreatic Acinar Cells, Determined by RNA-Sequencing Analysis

Intracellular Ca²⁺ homeostasis is commonly disrupted in acute pancreatitis. Sustained Ca²⁺ release from internal stores in pancreatic acinar cells (PACs), mediated by inositol triphosphate receptor (IP3R) and the ryanodine receptor (RyR), plays a key role in the initiation and propagation of acute pancreatitis. Pancreatitis induced by cerulein, an analogue of cholecystokinin, causes premature activation of digestive enzymes and enhanced accumulation of cytokines and Ca²⁺ in the pancreas and, as such, it is a good model of acute pancreatitis. High concentrations of the omega-3 fatty acid docosahexaenoic acid (DHA) inhibit inflammatory signaling pathways and cytokine expression in PACs treated with cerulein. In the present study, we determined the effect of DHA on key regulators of Ca²⁺ signaling in cerulein-treated pancreatic acinar AR42 J cells. The results of RNA-Sequencing (RNA-Seq) analysis showed that cerulein up-regulates the expression of IP3R1 and RyR2 genes, and that pretreatment with DHA blocks these effects. The results of real-time PCR confirmed that DHA inhibits cerulein-induced IP3R1 and RyR2 gene expression, and demonstrated that DHA pre-treatment decreases the expression of the Relb gene, which encodes a component of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcriptional activator complex, and the c-fos gene, which encodes a component of activator protein-1 (AP-1) transcriptional activator complex. Taken together, DHA inhibits mRNA expression of IP3R1, RyR2, Relb, and c-fos, which is related to Ca²⁺ network in cerulein-stimulated PACs.

TCDD‑induced chick cardiotoxicity is abolished by a selective cyclooxygenase‑2 (COX‑2) inhibitor NS398

Halogenated aromatic hydrocarbons, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are known to cause severe heart defects in avian species. However, the mechanism of TCDD-induced chick cardiovascular toxicity is unclear. In this study, we investigated cyclooxygenase-2 (COX-2) as a possible mechanism of TCDD-induced cardiotoxicity. Fertile chicken eggs were injected with TCDD and a COX-2 selective inhibitor, NS398, and we investigated chick heart failure on day 10. We found that the chick heart to body weight ratio and atrial natriuretic factor mRNA expression were increased, but this increase was abolished with treatment of NS398. In addition, the morphological abnormality of an enlarged ventricle resulting from TCDD exposure was also abolished with co-treatment of TCDD and NS398. Our results suggested that TCDD-induced chick heart defects are mediated via the nongenomic pathway and that they do not require the genomic pathway.

ANG II modulation of cardiac growth and remodeling in immature fetal sheep

ANG II increases fetal blood pressure and stimulates fetal heart growth; however, little is known regarding its direct effects on cardiomyocytes in vivo. We sought to determine whether ANG II stimulates heart growth and cardiomyocyte hypertrophy and/or hyperplasia in utero in the immature fetal heart independent of the effects on cardiac afterload. In twin gestation, fetal sheep at ∼100 days gestation (term 145 days), one fetus received a chronic (6 days) infusion of ANG II alone (50 μg·kg(-1)·min(-1)) or ANG II plus nitroprusside (NTP) to attenuate the increase in blood pressure; noninstrumented twins served as controls. ANG II alone, but not ANG II + NTP resulted in a significant increase in heart mass (left and right ventricle + septum, corrected for body weight) compared with controls. ANG II, but not ANG II+NTP, also significantly increased cardiomyocyte area compared with control and increased the percentage of binucleated myocytes. ANG II with or without concomitant infusion of NTP increased cardiac PCNA expression, a marker of proliferation. Steady-state protein expression of terminal mitogen-activated protein kinases, cyclin B1, cyclin E1, and p21 were similar among groups. We conclude that in vivo, ANG II increases fetal cardiac mass via cardiomyocyte hypertrophy, differentiation, and to a lesser extent hyperplasia. The effects of ANG II on hypertrophy appear dependent upon the increase in blood pressure (mechanical load), whereas effects on proliferation are load-independent.

Involvement of angiotensin II type 2 receptor (AT2R) signaling in human pancreatic ductal adenocarcinoma (PDAC): a novel AT2R agonist effectively attenuates growth of PDAC grafts in mice

We have recently discovered the potential involvement of angiotensin II type 2 receptor (AT2R) signaling in pancreatic cancer using AT2R deficient mice. To examine the involvement of AT2R expression in human PDAC, expressions of AT2R as well as the major angiotensin II receptor (type 1 receptor, AT1R) in human PDAC and adjacent normal tissue was evaluated by immunohistochemistry and real time PCR using surgically dissected human PDAC specimens. In immunohistochemical analysis, relatively strong AT1R expression was detected consistently in both normal pancreas and PDAC areas, whereas moderate AT2R expression was detected in 78.5% of PDAC specimens and 100% of normal area of the pancreas. AT1R, but not AT2R, mRNA levels were significantly higher in the PDAC area than in the normal pancreas. AT2R mRNA levels showed a negative correlation trend with overall survival. In cell cultures, treatment with a novel AT2R agonist significantly attenuated both murine and human PDAC cell growth with negligible cytotoxicity in normal epithelial cells. In a mouse study, administrations of the AT2R agonist in tumor surrounding connective tissue markedly attenuated growth of only AT2R expressing PAN02 murine PDAC grafts in syngeneic mice. The AT2R agonist treatment induced apoptosis primarily in tumor cells but not in stromal cells. Taken together, our findings offer clinical and preclinical evidence for the involvement of AT2R signaling in PDAC development and pinpoint that the novel AT2R agonist could serve as an effective therapeutic for PDAC treatment.

Role of microRNA-29b in angiotensin II-induced epithelial-mesenchymal transition in renal tubular epithelial cells

Angiotensin II (Ang II) has been proven to induce epithelial-mesenchymal transition (EMT). The aim of the present study was to determine the role of microRNA-29b (miR-29b) during Ang II-induced EMT. For this purpose, we used spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rats. The levels of Ang II and its receptor in the kidneys of the SHRs are significantly higher than those in the age-matched WKY rats. As shown by RT-qPCR, the expression of miR-29b in the renal cortex was lower in the SHRs than in the WKY rats. For in vitro experiments, NRK-52E renal tubular epithelial cells were treated with 10(-7) M Ang II; we found that the expression of miR-29b was decreased in the cells treated with Ang II. In addition, transfection of the NRK-52E cells with miR-29b inhibitor led to the downregulation of miR-29b in these cells, and increased the expression of transforming growth factor (TGF)-β, α-smooth muscle actin (α-SMA) and collagen I (Col I). Similar results were observed with the induction of Ang II expression in the NRK-52E cells. By contrast, the upregulation of miR-29b by transfection with miR-29b mimics inhibited the overexpression of these genes induced by Ang II. These results suggest that miR-29b plays an important role in Ang II-induced EMT.

Cellular trafficking determines the exon skipping activity of Pip6a-PMO in mdx skeletal and cardiac muscle cells

Cell-penetrating peptide-mediated delivery of phosphorodiamidate morpholino oligomers (PMOs) has shown great promise for exon-skipping therapy of Duchenne Muscular Dystrophy (DMD). Pip6a-PMO, a recently developed conjugate, is particularly efficient in a murine DMD model, although mechanisms responsible for its increased biological activity have not been studied. Here, we evaluate the cellular trafficking and the biological activity of Pip6a-PMO in skeletal muscle cells and primary cardiomyocytes. Our results indicate that Pip6a-PMO is taken up in the skeletal muscle cells by an energy- and caveolae-mediated endocytosis. Interestingly, its cellular distribution is different in undifferentiated and differentiated skeletal muscle cells (vesicular versus nuclear). Likewise, Pip6a-PMO mainly accumulates in cytoplasmic vesicles in primary cardiomyocytes, in which clathrin-mediated endocytosis seems to be the pre-dominant uptake pathway. These differences in cellular trafficking correspond well with the exon-skipping data, with higher activity in myotubes than in myoblasts or cardiomyocytes. These differences in cellular trafficking thus provide a possible mechanistic explanation for the variations in exon-skipping activity and restoration of dystrophin protein in heart muscle compared with skeletal muscle tissues in DMD models. Overall, Pip6a-PMO appears as the most efficient conjugate to date (low nanomolar EC₅₀), even if limitations remain from endosomal escape.

Transcriptional pathways and potential therapeutic targets in the regulation of Ncx1 expression in cardiac hypertrophy and failure

Changes in cardiac gene expression contribute to the progression of heart failure by affecting cardiomyocyte growth, function, and survival. The Na(+)-Ca(2+) exchanger gene (Ncx1) is upregulated in hypertrophy and is often found elevated in end-stage heart failure. Studies have shown that the change in its expression contributes to contractile dysfunction. Several transcriptional pathways mediate Ncx1 expression in pathological cardiac remodeling. Both α-adrenergic receptor (α-AR) and β-adrenergic receptor (β-AR) signaling can play a role in the regulation of calcium homeostasis in the cardiomyocyte, but chronic activation in periods of cardiac stress contributes to heart failure by mechanisms which include Ncx1 upregulation. Our studies have even demonstrated that NCX1 can directly act as a regulator of "activity-dependent signal transduction" mediating changes in its own expression. Finally, we present evidence that histone deacetylases (HDACs) and histone acetyltransferases (HATs) act as master regulators of Ncx1 expression. We show that many of the transcription factors regulating Ncx1 expression are important in cardiac development and also in the regulation of many other genes in the so-called fetal gene program, which are activated by pathological stimuli. Importantly, studies have revealed that the transcriptional network regulating Ncx1 expression is also mediating many of the other changes in genetic remodeling contributing to the development of cardiac dysfunction and revealed potential therapeutic targets for the treatment of hypertrophy and failure.

Oxidative stress-mediated effects of angiotensin II in the cardiovascular system

Angiotensin II (Ang II), an endogenous peptide hormone, plays critical roles in the pathophysiological modulation of cardiovascular functions. Ang II is the principle effector of the renin-angiotensin system for maintaining homeostasis in the cardiovascular system, as well as a potent stimulator of NAD(P)H oxidase, which is the major source and primary trigger for reactive oxygen species (ROS) generation in various tissues. Recent accumulating evidence has demonstrated the importance of oxidative stress in Ang II-induced heart diseases. Here, we review the recent progress in the study on oxidative stress-mediated effects of Ang II in the cardiovascular system. In particular, the involvement of Ang II-induced ROS generation in arrhythmias, cell death/heart failure, ischemia/reperfusion injury, cardiac hypertrophy and hypertension are discussed. Ca²⁺/calmodulin-dependent protein kinase II is an important molecule linking Ang II, ROS and cardiovascular pathological conditions.

Calcineurin regulation of cytoskeleton organization: a new paradigm to analyse the effects of calcineurin inhibitors on the kidney

Calcineurin is a serine/threonine phosphatase originally involved in the immune response but is also known for its role as a central mediator in various non-immunological intracellular signals. The nuclear factor of activated T cell (NFAT) proteins are the most widely described substrates of calcineurin, but ongoing work has uncovered other substrates among which are the cytoskeleton organizing proteins (i.e. cofilin, synaptopodin, WAVE-1). Control over cytoskeletal proteins is of outmost interest because the phenotypic properties of cells are dependent on cytoskeleton architecture integrity, while rearrangements of the cytoskeleton are implicated in both physiological and pathological processes. Previous works investigating the role of calcineurin on the cytoskeleton have focused on neurite elongation, myocyte hypertrophic response and recently in kidney cells structure. Nuclear factor of activated T cell activation is expectedly identified in the signalling pathways for calcineurin-induced cytoskeleton organization, however new NFAT-independent pathways have also been uncovered. The aim of this review is to summarize the current knowledge on the effects of calcineurin on cytoskeletal proteins and related intracellular pathways. These newly described properties of calcineurin on cytoskeletal proteins may explain some of the beneficial or deleterious effects observed in kidney cells associated with the use of the calcineurin inhibitors, cyclosporine and tacrolimus.

Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence

Angiotensin II type 1 receptor antagonists [ARBs (angiotensin receptor blockers)] are indicated for BP (blood pressure)-lowering, renal protection and cardioprotection in patients unable to tolerate ACEIs (angiotensin-converting enzyme inhibitors). A recent meta-analysis revealed an association between ARBs and tumour development, possibly due to enhancement of angiogenesis. However, published evidence is conflicting on the effects of ARBs on angiogenesis or the expansion of the existing vascular network. ARBs have been shown to exert primarily anti-angiogenic effects in basic science studies of cancer, retinopathy, peripheral artery disease and some models of cardiovascular disease. In animal and cellular models of myocardial infarction and stroke, however, ARB administration has been associated with robust increases in vascular density and improved recovery. The aim of the present review is to examine the angiogenic effects of ARBs in animal and cellular models of relevant disease states, including proposed molecular mechanisms of action of ARBs and the clinical consequences of ARB use.

Phorbol ester and endothelin-1 alter functional expression of Na+/Ca2+ exchange, K+, and Ca2+ currents in cultured neonatal rat myocytes

Endothelin-1 (ET-1) and activation of protein kinase C (PKC) have been implicated in alterations of myocyte function in cardiac hypertrophy and heart failure. Changes in cellular Ca2+ handling and electrophysiological properties also occur in these states and may contribute to mechanical dysfunction and arrhythmias. While ET-1 or PKC stimulation induces cellular hypertrophy in cultured neonatal rat ventricular myocytes (NRVMs), a system widely used in studies of hypertrophic signaling, there is little data about electrophysiological changes. Here we studied the effects of ET-1 (100 nM) or the PKC activator phorbol 12-myristate 13-acetate (PMA, 1 μM) on ionic currents in NRVMs. The acute effects of PMA or ET-1 (≤30 min) were small or insignificant. However, PMA or ET-1 exposure for 48-72 h increased cell capacitance by 100 or 25%, respectively, indicating cellular hypertrophy. ET-1 also slightly increased Ca2+ current density (T and L type). Na+/Ca2+ exchange current was increased by chronic pretreatment with either PMA or ET-1. In contrast, transient outward and delayed rectifier K+ currents were strongly downregulated by PMA or ET-1 pretreatment. Inward rectifier K+ current tended toward a decrease at larger negative potential, but time-independent outward K+ current was unaltered by either treatment. The enhanced inward and reduced outward currents also result in action potential prolongation after PMA or ET-1 pretreatment. We conclude that chronic PMA or ET-1 exposure in cultured NRVMs causes altered functional expression of cardiac ion currents, which mimic electrophysiological changes seen in whole animal and human hypertrophy and heart failure.

Effect of sodium tanshinone II A sulfonate on cardiac myocyte hypertrophy and its underlying mechanism

OBJECTIVE

To investigate the effects of sodium tanshinone II A sulfonate (STS) on the hypertrophy induced by angiotensin II (Ang II) in primary cultured neonatal rat cardiac myocytes.

METHODS

The effect of STS on cytotoxicity was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-3,5-phenytetrazoliumromide (MTT) assay. As indexes for cardiocyte hypertrophy, cell size was determined by phase contrast microscopy and protein synthesis rate was measured by 3H-leucine incorporation. The proto-oncogene c-fos mRNA expression of cardiocytes was assessed using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

STS could inhibit cardiocyte hypertrophy, increase the protein synthesis rate and enhance proto-oncogene c-fos mRNA expression in cardiocytes induced by Ang II (P<0.01), with an effect similar to that of Valsartan, the Ang II receptor antagonist.

CONCLUSION

STS can prevent the hypertrophy of cardiac myocytes induced by Ang II, which may be related to its inhibition of the expression of proto-oncogene c-fos mRNA.

Phospholipid-mediated signaling and heart disease

Cardiac hypertrophy, congestive heart failure, diabetic cardiomyopathy and myocardial ischemia-reperfusion injury are associated with a disturbance in cardiac sarcolemmal membrane phospholipid homeostasis. The contribution of the different phospholipases and their related signaling mechanisms to altered function of the diseased myocardium is not completely understood. Resolution of this issue is essential for both the understanding of the pathophysiology of heart disease and for determining if components of the phospholipid signaling pathways could serve as appropriate therapeutic targets. This review provides an outline of the role of phospholipase A2, C and D and subsequent signal transduction mechanisms in different cardiac pathologies with a discussion of their potential as targets for drug development for the prevention/treatment of heart disease.

Diacylglycerol kinase-epsilon restores cardiac dysfunction under chronic pressure overload: a new specific regulator of Galpha(q) signaling cascade

Galpha(q) protein-coupled receptor (GPCR) signaling pathway, which includes diacylglycerol (DAG) and protein kinase C (PKC), plays a critical role in cardiac hypertrophy. DAG kinase (DGK) catalyzes DAG phosphorylation and controls cellular DAG levels, thus acting as a regulator of GPCR signaling. It has been reported that DGKepsilon acts specifically on DAG produced by inositol cycling. In this study, we examined whether DGKepsilon prevents cardiac hypertrophy and progression to heart failure under chronic pressure overload. We generated transgenic mice with cardiac-specific overexpression of DGKepsilon (DGKepsilon-TG) using an alpha-myosin heavy chain promoter. There were no differences in cardiac morphology and function between wild-type (WT) and DGKepsilon-TG mice at the basal condition. Either continuous phenylephrine infusion or thoracic transverse aortic constriction (TAC) was performed in WT and DGKepsilon-TG mice. Increases in heart weight after phenylephrine infusion and TAC were abolished in DGKepsilon-TG mice compared with WT mice. Cardiac dysfunction after TAC was prevented in DGKepsilon-TG mice, and the survival rate after TAC was higher in DGKepsilon-TG mice than in WT mice. Phenylephrine- and TAC-induced DAG accumulation, the translocation of PKC isoforms, and the induction of fetal genes were blocked in DGKepsilon-TG mouse hearts. The upregulation of transient receptor potential channel (TRPC)-6 expression after TAC was attenuated in DGKepsilon-TG mice. In conclusion, these results demonstrate the first evidence that DGKepsilon restores cardiac dysfunction and improves survival under chronic pressure overload by controlling cellular DAG levels and TRPC-6 expression. DGKepsilon may be a novel therapeutic target to prevent cardiac hypertrophy and progression to heart failure.

Chromogranin B regulates calcium signaling, nuclear factor kappaB activity, and brain natriuretic peptide production in cardiomyocytes

Altered regulation of signaling pathways can lead to pathologies including cardiac hypertrophy and heart failure. We report that neonatal and adult cardiomyocytes express chromogranin B (CGB), a Ca(2+) binding protein that modulates Ca(2+) release by the inositol 1,4,5-trisphosphate receptor (InsP(3)R). Using fluorescent Ca(2+) indicator dyes, we found that CGB regulates InsP(3)-dependent Ca(2+) release in response to angiotensin II, an octapeptide hormone that promotes cardiac hypertrophy. ELISA experiments and luciferase reporter assays identified angiotensin II as a potent inducer of brain natriuretic peptide (BNP), a hormone that recently emerged as an important biomarker in cardiovascular disease. CGB was found to regulate angiotensin II-stimulated and basal secretion, expression and promoter activity of BNP that depend on the InsP(3)R. Moreover, we provide evidence that CGB acts via the transcription activity of nuclear factor kappaB in an InsP(3)/Ca(2+)-dependent manner but independent of nuclear factor of activated T cells. In vivo experiments further showed that cardiac hypertrophy induced by angiotensin II, a condition characterized by increased ventricular BNP production, is associated with upregulation of ventricular CGB expression. Overexpression of CGB in cardiomyocytes, in turn, induced the BNP promoter. The evidence presented in this study identifies CGB as a novel regulator of cardiomyocyte InsP(3)/Ca(2+)-dependent signaling, nuclear factor kappaB activity, and BNP production.

Angiotensin II directly triggers endothelial exocytosis via protein kinase C-dependent protein kinase D2 activation

Angiotensin II (AII) has been reported to induce leukocyte adhesion to endothelium through up-regulation of P-selectin surface expression. However, the underlying molecular and cellular mechanisms remain unknown. P-selectin is stored in Weibel-Palade bodies (WPBs), large secretory granules, in endothelial cells. In this study, we examined the role of protein kinase D (PKD), a newly identified regulator of protein transport, in AII-induced WPB exocytosis and the resultant P-selectin surface expression. We demonstrated that PKD2 was rapidly activated by AII in endothelial cells through phosphorylation of the activation loop at Ser744/748. AII-induced PKD2 activation correlated with increased P-selectin surface expression. Furthermore, AII-regulated PKD2 activation is protein kinase C (PKC) alpha-dependent. Importantly, knock-down of either PKD2 or PKCalpha expression inhibited AII-mediated P-selectin surface expression and monocyte adhesion. Our findings provide the first evidence that stimulation of P-selectin surface expression via PKCalpha-dependent PKD2 activation could be an important mechanism in the early onset of AII-initiated endothelial adhesiveness.

Role of diacylglycerol kinase in cellular regulatory processes: A new regulator for cardiomyocyte hypertrophy

Diacylglycerol (DAG) kinase (DGK) phosphorylates and converts DAG to phosphatidic acid. DGK regulates cellular DAG levels and attenuates DAG signaling. The 10 mammalian DGK isoforms have been identified to date. In cardiac myocytes, DGKalpha, epsilon, and zeta are expressed, and DGKzeta is the predominant isoform. DGKzeta inhibits protein kinase C (PKC) activation and subsequent hypertrophic programs in response to endothelin-1 (ET-1) in neonatal rat cardiomyocytes. DGKzeta blocks cardiac hypertrophy induced by G protein-coupled receptor agonists and pressure overload in vivo. DGKzeta attenuates ventricular remodeling and improves survival after myocardial infarction. These data provide a novel insight for subcellular mechanisms of cardiac hypertrophy and heart failure, and DGKzeta may be a new therapeutic target to prevent cardiac hypertrophy and progression to heart failure.

Modeling hypertrophic IP3 transients in the cardiac myocyte

Cardiac hypertrophy is a known risk factor for heart disease, and at the cellular level is caused by a complex interaction of signal transduction pathways. The IP3-calcineurin pathway plays an important role in stimulating the transcription factor NFAT which binds to DNA cooperatively with other hypertrophic transcription factors. Using available kinetic data, we construct a mathematical model of the IP3 signal production system after stimulation by a hypertrophic alpha-adrenergic agonist (endothelin-1) in the mouse atrial cardiac myocyte. We use a global sensitivity analysis to identify key controlling parameters with respect to the resultant IP3 transient, including the phosphorylation of cell-membrane receptors, the ligand strength and binding kinetics to precoupled (with G(alpha)GDP) receptor, and the kinetics associated with precoupling the receptors. We show that the kinetics associated with the receptor system contribute to the behavior of the system to a great extent, with precoupled receptors driving the response to extracellular ligand. Finally, by reparameterizing for a second hypertrophic alpha-adrenergic agonist, angiotensin-II, we show that differences in key receptor kinetic and membrane density parameters are sufficient to explain different observed IP3 transients in essentially the same pathway.

Dose and time-dependent apoptotic effects by angiotensin II infusion on left ventricular cardiomyocytes

OBJECTIVE

To gain insight into the regulation of cardiac apoptosis we studied the dose-response and time-course effects of angiotensin II (Ang II) infusion on ventricular cardiomyocyte apoptosis and on the expression of Bax and Bcl-2 genes and proteins.

STUDY DESIGN AND METHODS

In the dose-response study, Ang II was infused subcutaneously at doses of 100, 200, 400, 800 and 1200 ng/kg per min for 14 days. In the time-course study, rats infused with Ang II at doses of 200 and 400 ng/kg per min were followed for 7 and 14 days. The cardiomyocyte apoptotic density was assessed by DNA end labelling (terminal deoxynucleotide nick-end labelling; TUNEL). Gene and protein expression of Bcl-2 and Bax were evaluated by reverse transcriptase-polymerase chain reaction and by Western blots.

RESULTS

Systolic blood pressure and left ventricular mass were increased in a dose-dependent manner in Ang II-infused rats. A statistically significant increase in the rate of cardiac apoptosis and pro-apoptotic changes of Bcl-2 and Bax gene and protein expression was observed when high doses of Ang II (800-1200 ng/kg per min) were infused. A positive correlation of apoptotic density with Bax and a negative correlation with Bcl-2 and Bcl-2/Bax ratio were found. Cardiac apoptosis was greatly influenced by the timing of Ang II infusion. Losartan-treated Ang II-infused rats exhibited normalized systolic blood pressure, left ventricular weight, apoptosis, and Bax and Bcl-2 levels.

CONCLUSIONS

Our results are consistent with the pathophysiological role of Ang II in induction of cardiac apoptosis, and explain the cardioprotective effect of Ang II receptor antagonists.

Phospholipid-mediated signaling systems as novel targets for treatment of heart disease

The phospholipases associated with the cardiac sarcolemmal (SL) membrane hydrolyze specific membrane phospholipids to generate important lipid signaling molecules, which are known to influence normal cardiac function. However, impairment of the phospholipases and their related signaling events may be contributory factors in altering cardiac function of the diseased myocardium. The identification of the changes in such signaling systems as well as understanding the contribution of phospholipid-signaling pathways to the pathophysiology of heart disease are rapidly emerging areas of research in this field. In this paper, I provide an overview of the role of phospholipid-mediated signal transduction processes in cardiac hypertrophy and congestive heart failure, diabetic cardiomyopathy, as well as in ischemia-reperfusion. From the cumulative evidence presented, it is suggested that phospholipid-mediated signal transduction processes could serve as novel targets for the treatment of the different types of heart disease.

Expression of MAK-V/Hunk in renal distal tubules and its possible involvement in proliferative suppression

MAK-V/Hunk is an SNF1-related serine/threonine kinase which was previously shown to be highly expressed in the mammary gland and central nervous system. In this study, we found MAK-V/Hunk is abundantly and specifically expressed in the thick ascending limbs and distal convoluted tubules (DCT) of the kidney from the embryonic stage to the adult stage. We demonstrated that dietary salt depletion significantly enhances renal MAK-V/Hunk mRNA levels compared with a normal-salt diet. To analyze the possible renal cellular function of this kinase, we employed mouse distal convoluted tubule (mDCT) cells. The results of reverse transcriptase-polymerase chain reaction and Western blot analysis revealed that MAK-V/Hunk is expressed endogenously in mDCT cells. Overexpression of MAK-V/Hunk by adenoviral gene transfer significantly inhibited the ANG II-induced stimulation of c-fos gene transcription and suppressed the ANG II-mediated increases in transforming growth factor-beta production into the medium. This phenomenon was accompanied by inhibition of ANG II-induced activation of BrdU incorporation. On the other hand, the MAK-V/Hunk knockdown by siRNA activated the ANG II-induced c-fos gene expression. In the consecutive sections stained for MAK-V/Hunk and AT(1) receptor, MAK-V/Hunk-immunopositive distal tubules expressed the AT(1) receptor. This is the first report on the intrarenal localization of MAK-V/Hunk and its cellular function in renal tubular cells.

ACE inhibitors in pediatric patients with heart failure

This article reviews reports of ACE inhibitor use in pediatric heart failure and summarizes the present implications for clinical practice. Captopril, enalapril, and cilazapril are orally active ACE inhibitors, and widely used in pediatric cardiology, although more than ten other ACE inhibitors have been applied clinically in adults. Effects of ACE inhibitors on the renin-angiotensin-aldosterone system in pediatric patients are similar to those in adults. ACE inhibitors lower aortic pressure and systemic vascular resistance, do not affect pulmonary vascular resistance significantly, and lower left atrial and right atrial pressures in pediatric patients with heart failure. In infants with a large ventricular septal defect and pulmonary hypertension, ACE inhibitors decrease left-to-right shunt in those infants with elevated systemic vascular resistance. ACE inhibitors induce a small increase in left ventricular ejection fraction, left ventricular fractional shortening, and systemic blood flow in children with left ventricular dysfunction, mitral regurgitation, and aortic regurgitation. These beneficial effects usually persist long term without the development of tolerance. Therapeutic trials of ACE inhibitors have been reported in children with heart failure and divergent hemodynamics, including myocardial dysfunction, left-to-right shunt, such as large ventricular septal defect and pulmonary hypertension, aortic or mitral regurgitation, and Fontan circulation. Hypotension and renal failure usually occur within 5 days after starting ACE inhibition or increasing the dose and, in most cases, recovery is seen after reduction or cessation of the drug. With all ACE inhibitors, smaller doses are administered initially to prevent excessive hypotension, and doses are increased gradually to the target dose. Captopril is administered orally, usually every 8 hours. Daily doses range from 0.3 to 1.5 mg/kg in children. Enalapril is administered orally, once or twice a day, and daily doses range from 0.1 to 0.5 mg/kg. Enalaprilat is administered intravenously, one to three times a day, in doses ranging from 0.01 to 0.05 mg/kg/dose. For the treatment of chronic heart failure in children, ACE inhibitors are essential along with other medications including diuretics, digoxin, and beta-blockers (beta-adrenoceptor antagonists).

Effect of chlorpromazine on bone sialoprotein (BSP) gene transcription

Bone sialoprotein (BSP), an early marker of osteoblast differentiation. Whereas physical forces may play an important role in the regulation of bone cell function, little is known about how cells are able to sense mechanical loads. Chlorpromazine, a tranquilizing agent for treatments of psychiatric disorders, mimics hypotonic stress and causes membrane deformation. Application of 10 microg/ml of chlorpromazine suppressed BSP mRNA levels after 12 and 24 h in osteoblast-like ROS17/2.8 cells and rat stromal bone marrow cells (SBMC-D8). Chlorpromazine (10 microg/ml) decreased luciferase activity of the construct (pLUC3; -116 to +60 of the rat BSP gene promoter) after 12 h, the effect was inhibited by the tyrosine kinase inhibitor herbimycin A (HA) and MAP kinase kinase inhibitor U0126. Introduction of 2-bp mutation in the pLUC3 construct showed that the chlorpromazine effects were mediated by cAMP response element (CRE) and FGF2 response element (FRE). In gel shift assays, using radiolabeled double-stranded CRE and FRE oligonucleotides, which revealed decreased binding of nuclear proteins from chlorpromazine-stimulated cells. These studies, therefore, show that chlorpromazine suppresses BSP gene transcription through tyrosine and MAP kinases-dependent pathways and that the chlorpromazine effects are mediated by CRE and FRE elements in the proximal promoter of the BSP gene.

Role of the JAK/STAT signaling pathway in diabetic nephropathy

Excessive cellular growth is a major contributor to pathological changes associated with diabetic nephropathy. In particular, high glucose-induced growth of glomerular mesangial cells is a characteristic feature of diabetes-induced renal complications. Glomerular mesangial cells respond to traditional growth factors, although in diabetes this occurs in the context of an environment enriched in both circulating vasoactive mediators and high glucose. For example, the vasoactive peptide ANG II has been implicated in the pathogenesis of diabetic renal disease, and recent findings suggest that high glucose and ANG II activate intracellular signaling processes, including the polyol pathway and generation of reactive oxygen species. These pathways activate the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling cascades in glomerular mesangial cells. Activation of the JAK/STAT signaling cascade can stimulate excessive proliferation and growth of glomerular mesangial cells, contributing to diabetic nephropathy. This review focuses on some of the key elements in the diabetic microenvironment, especially high glucose and the accumulation of advanced glycoxidation end products and considers their impact on ANG II and other vasoactive peptide-mediated signaling events in vitro and in vivo.

Hemoglobin cycling in hemodialysis patients treated with recombinant human erythropoietin

BACKGROUND

Treatment with recombinant human erythropoietin (rHuEPO) has been a major advance for the management of anemia in patients on hemodialysis. Therapy, however, is often observed to be associated with recurrent cyclic fluctuations in hemoglobin levels. The purpose of this analysis was to describe the phenomenology of hemoglobin cycling during rHuEPO treatment.

METHODS

Data were analyzed for 281 hemodialysis patients treated at Winthrop-University Hospital Dialysis Centers between 1998 and 2003. Eligible patients' first full 1-year period with less than 10 hospital days was studied. Hemoglobin cycling (cycles with amplitude >1.5 g/dL and duration >8 weeks) and excursions (half of one full cycle) were analyzed.

RESULTS

Greater than 90% of patients experienced hemoglobin cycling. The mean number of hemoglobin excursions was 3.1 +/- 1.1 per patient/year. The mean amplitude per hemoglobin excursion was 2.51 +/- 0.89 g/dL. The mean duration of hemoglobin excursions was 10.3 +/- 5.1 weeks. Factors associated with initiation of up excursions included increases in rHuEPO dose (84%), intravenous iron treatment initiation or increase in dose (27%), posthospital discharge (36%), factors associated with down excursions included rHuEPO dose hold (15%) or dose reduction (62%), infection (6%), discontinuation of intravenous iron therapy (5%), and hospitalization (14%). Patients with frequent hemoglobin cycling (>two full cycles per year) were characterized as being more responsive to rHuEPO [index of EPO responsiveness (ERI) 1036 +/- 659 compared to 1992 +/- 701 for other patients] (P = 0.02).

CONCLUSION

Hemoglobin cycling is a common occurrence in rHuEPO-treated hemodialysis patients. It is most closely associated with frequent rHuEPO dose changes, hospitalization, and iron treatment practices.

Convergence of protein kinase C and JAK-STAT signaling on transcription factor GATA-4

Angiotensin II (AII), a potent vasoactive hormone, acts on numerous organs via G-protein-coupled receptors and elicits cell-specific responses. At the level of the heart, AII stimulation alters gene transcription and leads to cardiomyocyte hypertrophy. Numerous intracellular signaling pathways are activated in this process; however, which of these directly link receptor activation to transcriptional regulation remains undefined. We used the atrial natriuretic factor (ANF) gene (NPPA) as a marker to elucidate the signaling cascades involved in AII transcriptional responses. We show that ANF transcription is activated directly by the AII type 1 receptor and precedes the development of myocyte hypertrophy. This response maps to STAT and GATA binding sites, and the two elements transcriptionally cooperate to mediate signaling through the JAK-STAT and protein kinase C (PKC)-GATA-4 pathways. PKC phosphorylation enhances GATA-4 DNA binding activity, and STAT-1 functionally and physically interacts with GATA-4 to synergistically activate AII and other growth factor-inducible promoters. Moreover, GATA factors are able to recruit STAT proteins to target promoters via GATA binding sites, which are sufficient to support synergy. Thus, STAT proteins can act as growth factor-inducible coactivators of tissue-specific transcription factors. Interactions between STAT and GATA proteins may provide a general paradigm for understanding cell specificity of cytokine and growth factor signaling.

Pitavastatin Inhibits Cardiac Hypertrophy in a Rat Model of Progressive Renal Injury

Increased cardiovascular mortality is an unresolved problem of chronic renal failure. Cardiac hypertrophy, observed in many patients with chronic renal failure, is a major risk factor for cardiovascular death. The purpose of the present study was to examine the effects of pitavastatin on cardiac hypertrophy in a progressive renal injury rat model by subtotal nephrectomy (SNx). Because we previously reported that angiotensin II played a pivotal role in cardiac hypertrophy of SNx rats, we first investigated the effects of pitavastatin on angiotensin II-induced activation of extracellular signal-regulated kinase (ERK) and serum response element (SRE) DNA-binding activity using neonatal rat cardiomyocytes. Angiotensin II-induced ERK activation was attenuated by pretreatment with pitavastatin. Luciferase assay revealed that angiotensin II-induced increase in SRE DNA-binding activity was inhibited by pitavastatin. We next examined the effect of pitavastatin on cardiac hypertrophy of SNx rats in vivo. Treatment with pitavastatin prevented ERK activation and cardiac hypertrophy in SNx rats without changes in blood pressure. The increased expression of atrial natriuretic factor mRNA in SNx rat hearts was significantly attenuated by the treatment with pitavastatin. These results suggest that pitavastatin has a beneficial effect on cardiac hypertrophy in renal failure through preventing the activation of ERK.

Identification of a novel 5-base pair deletion in calcineurin B (PPP3R1) promoter region and its association with left ventricular hypertrophy

BACKGROUND

Calcineurin is a calcium/calmodulin-regulated protein phosphatase that functions as a key mediator of hypertrophic response of the heart. Calcineurin B (CnB) is a regulatory subunit of calcineurin and is important for the phosphatase activity.

METHODS

We identified a novel 5-base pair (bp) insertion/deletion (5I/5D) polymorphism within the CnB promoter region and investigated its association with left ventricular hypertrophy (LVH) in 368 severe hypertensive participants (53% African Americans) in the Hypertension Genetic Epidemiology Network study. Traditionally defined LVH was identified by LV mass index >50 g/m(2.7) in men and >47 g/m(2.7) in women. Left ventricular mass predicted from sex, stroke work, and height(2.7) was calculated according to an equation derived from a normal population, and inappropriately high LV mass was defined as observed/predicted LV mass >1.28 based on the equation.

RESULTS

The CnB 5I/5D variation was not significantly associated with the traditionally defined LVH. However, there was a significant association between the CnB 5I/5D polymorphism and presence of inappropriately high LV mass. The ethnicity-adjusted ORs for the 5I/5D and 5D/5D genotypes compared with the 5I/5I genotype was 1.23 (95% CI 0.66-2.28) and 3.05 (95% CI 1.28-7.29) (P = .02 for trend test). This association was independent of age, sex, body mass index, heart rate, prevalent coronary heart disease, and/or diabetes and antihypertensive medications.

CONCLUSIONS

The 5-base pair deletion within the CnB gene may cause excessive LV growth beyond the level appropriate for cardiac workload when exposed to severe hypertension or may be in linkage disequilibrium with the causal mutation.

Inhibitory effects of interferon-γ on myocardial hypertrophy

Prostaglandin F(2alpha) (PGF(2alpha)) plays an important role in pathologic cardiac growth. After testing several immune cytokines, we found that interferon-gamma (IFN-gamma) inhibited responsiveness of adult myocytes to PGF(2alpha). The present study was designed to test the hypothesis that IFN-gamma inhibits cardiac hypertrophy induced by PGF(2alpha). Incubation of cultured adult rat cardiac myocytes with PGF(2alpha) caused cell spreading, which was inhibited by IFN-gamma. The inhibitory effect was not affected by nitric oxide (NO) synthase inhibitors. In addition, administration of fluprostenol, a more selective agonist at the PGF(2alpha) receptor, induced cardiac hypertrophy in rats. Chronic treatment with IFN-gamma inhibited this myocardial growth, and the inhibitory effect of IFN-gamma was not accompanied by an increase in myocardial NO synthase gene expression. Further, abdominal aortic constriction resulted in a substantial increase in heart, ventricular and left ventricular weights to BW ratio that was significantly attenuated by treatment with IFN-gamma. The results demonstrate that IFN-gamma inhibits the in vitro and in vivo effects of PGF(2alpha) on cardiac hypertrophy, and that the mechanism of action is likely independent of NO production. IFN-gamma also attenuated cardiac hypertrophy induced by pressure overload, suggesting that PGF(2alpha) plays a role in the pathogeneses of this severe type of cardiac hypertrophy.

Effects of cardiac support device on reverse remodeling: molecular, biochemical, and structural mechanisms

Progressive left ventricular (LV) dilation is a characteristic feature of heart failure and is invariably associated with poor long-term prognosis. This review discusses observations made in dogs with chronic heart failure using a passive mechanical containment device, the Acorn Cardiac Support Device (CSD), which is designed to prevent progressive LV enlargement. Studies have shown that, in addition to preventing LV dilation, long-term therapy with the CSD also improved LV ejection fraction, tended to normalize LV shape, reduced LV wall stress, and reduced or eliminated functional mitral regurgitation. At the cellular level, the CSD attenuates cardiomyocyte hypertrophy, reduced oxygen diffusion distance and downregulated stretch response proteins. The CSD also improved calcium cycling within the sarcoplasmic reticulum and upregulated mRNA gene expression for alpha-myosin heavy chain. These findings, when viewed in concert, provide an explanation for mechanisms that may be responsible for the improvement in LV function seen in dogs with heart after long-term CSD therapy.

Differential changes in phospholipase D and phosphatidate phosphohydrolase activities in ischemia–reperfusion of rat heart

Phospholipase D (PLD2) produces phosphatidic acid (PA), which is converted to 1,2 diacylglycerol (DAG) by phosphatidate phosphohydrolase (PAP2). Since PA and DAG regulate Ca(2+) movements, we examined PLD2 and PAP2 in the sarcolemma (SL) and sarcoplasmic reticular (SR) membranes from hearts subjected to ischemia and reperfusion (I-R). Although SL and SR PLD2 activities were unaltered after 30 min ischemia, 5 min reperfusion resulted in a 36% increase in SL PLD2 activity, whereas 30 min reperfusion resulted in a 30% decrease in SL PLD2 activity, as compared to the control value. SR PLD2 activity was decreased (39%) after 5 min reperfusion, but returned to control levels after 30 min reperfusion. Ischemia for 60 min resulted in depressed SL and SR PLD2 activities, characterized with reduced V(max) and increased K(m) values, which were not reversed during reperfusion. Although the SL PAP2 activity was decreased (31%) during ischemia and at 30 min reperfusion (28%), the SR PAP2 activity was unchanged after 30 min ischemia, but was decreased after 5 min reperfusion (25%) and almost completely recovered after 30 min reperfusion. A 60 min period of ischemia followed by reperfusion caused an irreversible depression of SL and SR PAP2 activities. Our results indicate that I-R induced cardiac dysfunction is associated with subcellular changes in PLD2 and PAP2 activities.

The novel angiotensin II type 1 receptor (AT1R)-associated protein ATRAP downregulates AT1R and ameliorates cardiomyocyte hypertrophy

Activation of angiotensin II (Ang II) type 1 receptor (AT1R) signaling is reported to play an important role in cardiac hypertrophy. We previously cloned a novel molecule interacting with the AT1R, which we named ATRAP (for Ang II type 1 receptor-associated protein). Here, we report that overexpression of ATRAP significantly decreases the number of AT1R on the surface of cardiomyocytes, and also decreases the degree of p38 mitogen-activated protein kinase phosphorylation, the activity of the c-fos promoter and protein synthesis upon Ang II treatment. These results indicate that ATRAP significantly promotes downregulation of the AT1R and further attenuates certain Ang II-mediated hypertrophic responses in cardiomyocytes.